The present invention relates generally to surgical tissue fixation equipment and systems and, more particularly, to bioabsorbable fixation systems including bodily tissue fixation hardware comprising biocompatible, bioabsorbable (resorbable) polymeric or composite plates and fasteners for securing the plates to bodily tissue for fixation thereof, and an installation instrument which triggers (strikes) fasteners one after one into through-bores (holes) made through the plate and into the underlying bodily tissue.
Traditional orthopedic and traumatological and cranio-maxillo-facial fixation systems to facilitate bone fracture healing (osteosynthesis) or soft tissue-to-bone healing typically employ metallic hardware, e.g., plates, screws, rods and the like, formed of biocompatible, corrosion resistant metals such as titanium and stainless steel. Typical metallic plates are described, e.g., in the book F. Sxc3xa9quin and R. Texhammar, AO/ASIF Instrumentation, Springer-Verlag, Berlin, Heidelberg, 1981, p. 21-22, 55-79, 107-108, 117-122, the entire disclosure of which is incorporated herein by way of this reference. While such systems are generally effective for their intended purposes, they possess a number of inherent shortcomings. For example, metal release to the surrounding tissues (see, e.g., L.-E. Moberg et al. Int. J. Oral. Maxillofac. Surg. 18 (1989) p. 311-314, the entire disclosure of which is incorporated herein by reference) has been reported. Other reported shortcomings are stress shielding (e.g., P. Paavolainen et al., Clin Orthop. Rel. Res. 136 (1978) 287-293, the entire disclosure of which is incorporated herein by reference) and growth restriction in young individuals (e.g., K. Lin et al., Plast. Reconstr. Surg. 87 (1991) 229-235, the entire disclosure of which is incorporated herein by reference). In infants and young children there is the risk that metallic plates and screws sink, as a consequence of skull bone growth, into and below the cranial bone threatening brain (J. Fearon et al., Plast. Reconstr. Surg. 4 (1995) 634-637, the entire disclosure of which is incorporated herein by reference). Therefore, it is recommended generally that non-functional implants should be removed, at least in growing individuals (see, e.g., C. Lindqvist, Brit. J. Oral Maxillofac. Surg. 33 (1995) p. 69-70, the entire disclosure of which is incorporated herein by reference).
Especially in maxillofacial and in cranial surgery metallic mini plates are popular (see, e.g., W. Muhlbauer et al., Clin. Plast. Surg. 14 (1987) 101-111; A. Sadove and B. Eppleg, Ann. Plast. Surg. 27 (1991) 36-43; R. Suuronen, Biodegradable Self-reinforced Polylactide Plates and Screws in the Fixation of Osteotomies in the Mandible, Doctoral Thesis, Helsinki University, Helsinki, 1992, p. 16, the entire disclosures of which are incorporated herein by reference; and see the references cited in the previous references). Mini plates are small, thin, narrow plates, which have holes for screw fixation. They are located typically on bone perpendicularly over the fracture to fix the bone mass on both sides of the fracture to each others. Typical geometries of mini plates are described, e.g., in U.S. Pat. No. 5,290,281, in FIGS. 6A-6F, the entire disclosure of which is incorporated herein by reference.
The main advantage of metallic plates, screws, etc. (like titanium, stainless steel and cobalt chrome molybdenum plates or screws), is that they are strong, and tough. Ductile metal plates can be deformed or shaped (bent) at room temperature in an operation room by hand or with special instruments to the shape of a form that corresponds to the surface topography of the bone to be fixed, so that the plate can be fixed flush on the bone surface to which the plate is applied.
Because of the shortcomings of metallic plates, bioabsorbable plates have been developed for fracture fixation. Longitudinal, six-hole plates were developed by Eitenmxc3xcller et al. for orthopaedic animal studies (European Congress on Biomaterials, Abstracts, Instituto Rizzoli, Bologna, 1986, p. 94, the entire disclosure of which is incorporated herein by reference). However, because of inadequate strength, some of the plates were broken in animal experiments involving fracture fixation.
A particular advantage of bioabsorbable plates is that they can be provided with openings for the insertion of surgical fasteners (like screws) therethrough, while also allowing means to permit the formation of additional fastener openings therethrough during a surgical procedure at the surgeon""s discretion, as has been described in European Patent specification EP 0 449 867 B1, the entire disclosure of which is incorporated herein by reference.
However, the main disadvantage of most prior art bioabsorbable plates is that they can be deformed (bent) permanently and safely only at elevated temperatures above the glass transition temperature (Tg) of the bioabsorbable polymer, as has been described, e.g., in EP 0 449 867 B1, U.S. Pat. No. 5,569,250 and U.S. Pat. No. 5,607,427, the entire disclosures of which are incorporated herein by reference. Below the respective glass transition temperatures of the bioabsorbable polymers from which they are made, most prior art bioabsorbable plates are brittle and break easily when deformed. Only at temperatures above the Tg of the bioabsorbable polymer from which a given plate is made does the molecular structure of most prior art plates have enough mobility to allow shaping and bending of the plate, without the risk of breaking.
Because the thermal conductivity of most polymeric materials is generally poor, both heating and cooling of bioabsorbable plates are slow processes. Therefore, the clinical use of such prior art plates is tedious, slow and complex, especially if the surgeon must shape the plate several times to make it fit exactly to the form of the bone to be fixed.
K. Bessho et al., J. Oral. Maxillofac. Surg. 55 (1997) 941-945, the entire disclosure of which is incorporated herein by reference, describe a bioabsorbable poly-L-lactide miniplate and screw system for osteosynthesis in oral and maxillofacial surgery. The plates of that reference also must be heated by immersion in a hot sterilized physiologic salt solution, or by the application of hot air, until they become plastic, and only then can those plates be fitted to the surface of the bone being repaired.
EP 0 449 867 B1, the entire disclosure of which is incorporated herein by reference, describes a plate for fixation of a bone fracture, osteotomy, arthrodesis, etc., said plate being intended to be fixed on bone with at least one fixation device, like a screw, rod, clamp or some other corresponding device. The plates of that reference comprise at least two essentially superimposed plates, so as to provide a multilayer plate construction, so that the individual plates of said multilayer plate construction are flexible to provide a change of form of said multilayer plate construction to substantially assume the shape of the bone surface under the operation conditions. That change of form is accomplished by means of an external force, such as by hand and/or by a bending instrument directed to said multilayer plate construction, whereby each individual plate assumes the position of its own with respect to other individual plates by differential motion along the surfaces of the coinciding plates.
Although the above multilayer plate can fit the curved bone surface without heating of the individual plates, the clinical use of such multilayer plates is tedious, because the single plates easily slip in relation to each other before fixation. Additionally the thickness of multilayer plate system easily becomes too thick for cranio maxillofacial applications, causing cosmetic disturbance and increased risks of foreign body reaction.
To avoid the above mentioned shortcomings in the prior art devices, U.S. Pat. Appl. Ser. No. 09/036,259, the entire disclosure of which is incorporated herein by reference, describes strong and tough, uni- and/or biaxially oriented and/or self-reinforced bioabsorbable plates, which are deformable at room temperature, like in operation room conditions, prior to implantation in a patient. The plates described in that application retain their deformed (bent or shaped) form so well at body temperature in tissue conditions (e.g., when implanted on a patient""s bone) that they keep the fixed bone fragments in the desired position to facilitate bone fracture healing. When using such plates surgically, the surgeon can bend (and rebend) the plate easily in operation conditions, without needing the slow and tedious heating-bending-cooling procedure of the prior art plates.
While the clinical use of the bioabsorbable plates described in U.S. Pat. Appl. Ser. No. 09/036,259 significantly reduces operation time in comparison to the clinical use of other prior art bioabsorbable plates, the fixation of plates on tissue or bone is still a slow and tedious process. Prior art fixation techniques mainly use screws or screw-type fasteners for plate fixation. However, turning of screws or screw-type fasteners into drill holes is a slow process. For example, in a single maxillo-cranio-facial operation, tens of screws may be used for plate fixation and such an operation may demand hours to complete. On the other hand, manual use of other types of fasteners, like expansion bolts (pins), or plugs or rivets is also a slow and risky process. For example, manual hammering of fasteners, like those described in U.S. Pat. No. 5,261,914 or U.S. Pat. No. 5,607,427, the entire disclosures of which are incorporated herein by reference, can easily be done too strongly, so that the head of the fastener and/or plate and/or underlying tissue(s) is (are) damaged.
Two-component fasteners, like expansion bolts or plugs (such as those described in H. Pihlajamxc3xa4ki et al. ,: A biodegradable expansion plug for the fixation of fractures of the medial malleolus, Ann Chir Gyn 83: 47-52, 1994, the entire disclosure of which is incorporated herein by reference) or pop rivet-type fasteners can be complicated and risky to use because strong expansion of a part of such a fastener can cause extensive compression to the surrounding bone, leading to bone necrosis.
A need, therefore, still exists for a surgical tissue fixation system comprising (a) a bioabsorbable (bioresorbable or biodegradable) plate, which is strong, tough and thin, substantially rigid and deformable (either at room temperature or at an elevated temperature); (b) a bioabsorbable fastener adapted for insertion into through-bores (drill holes) in the bioabsorbable plate, to secure the plate to underlying bodily tissue in a rapid and safe manner; and (c) an installation instrument which installs (e.g., by triggering or striking) the fasteners one after another rapidly, securely and with a minimal trauma into the through-bores made through the plate and into the underlying bodily tissue.
A need also exists for a surgical tissue fixation system comprising a bioabsorbable plate, bioabsorbable fasteners and an installation instrument, which triggers the fasteners one after another into the drill holes made through the plate and optionally also into the underlying bodily tissue, with a single strike or with several consecutive strikes, without the need of turning the fastener around its long axis during installation.
A need also exists for a surgical tissue fixation system comprising a bioabsorbable plate, bioabsorbable fasteners and an installation instrument, which triggers the fasteners one after another precisely into the drill holes in plates, so that the lower surface of the fastener head mates exactly with the upper surface of the plate (or with the countersink surface in the upper part of the drill hole in the plate).
A need also exists for a curved cannula for attaching to the above fixation instrument, to allow application of the fasteners onto bone in areas, e.g., such as the posterior mandible or subcutaneous spaces, where there is no access with straight upright instrumentation.
In accordance with the present invention, there is provided a surgical tissue fixation system, including a bioabsorbable plate and a bioabsorbable fastener to secure the plate to underlying bodily tissue and an installation tool which triggers the fasteners one after another through drill holes made through the plate and into the underlying bodily tissue. The plate and fastener equipment is particularly adapted for fixating fractured or severed bones, or for affixing a ligament, tendon or connective tissue on a bone or into a drillhole in a bone, to promote rapid and beneficial healing of the treated bones and/or tissues.
In a preferred embodiment of the invention, the installation instrument cooperates as part of a surgical system with one or more specially configured plates, fabricated from bioabsorbable polymeric or composite material, wherein the plates can be secured by a surgeon via a plurality of fasteners to a bone, cartilage, tendon, connective tissue or other bodily tissue being repaired. Other details, objects and advantages of the present invention will become apparent from the following description of the presently preferred embodiments and presently preferred methods of practicing the invention.